Coal-water slurries are well known to those skilled in the art. Some of them have a high solids content and can be burned directly without being dewatered. Some of them have a low viscosity and can be readily pumped through pipelines. Some of them require a substantial amount of energy to prepare. Some of them are stable and can be stored for long periods of time in a quiescent state before being burned. However, there are no prior art coal-water slurries known to applicant which combine the properties of high solids content, low viscosity, and stability.
The prior art teaches that high density coal-water slurries have high viscosities and are substantially unpumpable. Thus, as is taught in U.S. Pat. No. 4,052,169 of Cole et al., a coal-water slurry containing more than 60 weight percent of coal is " . . . difficult to pump" (lines 40-44 of Column 2). Thus, U.S. Pat. No. 4,104,035 of Cole et al., teaches that "As the solids content increases above this range the slurry becomes increasingly difficult to pump and at about 50% solids content it is unpumpable" (lines 30-33 of Column 1).
U.S. Pat. No. 4,242,098 teaches that, in general, coal-water slurries containing more than about 50 weight percent of coal are unstable, stating that "Aqueous slurries of finely ground coal containing more than about 55 weight percent solids are difficult to transport using conventional slurry pumps because as the solids level is increased above about 50 weight percent the water and solids tend to separate causing coal particles to build up in various areas throughout the pumping system" (Column 1, lines 15-21).
U.S. Pat. No. 3,762,887 discloses a coal-water slurry containing 54-69 volume percent of coal and 46-31 volume percent of water. The coal particles in the slurry have a specified particle size distribution such that substantially all of the particles pass through a 4 mesh Tyler Standard Screen and between 18 and 33 percent pass through a 325 mesh (44 microns) Tyler Standard Screen. The patentees teach that the viscosity of their slurry " . . . is in the range of that of hot Bunker C fuel oil" (Column 3, lines 13-14).
It is an object of this invention to provide a grinding mixture which can be used to prepare a high density, stable, carbonaceous solids-liquid slurry which has relatively low viscosity. It is yet another object of this invention to provide a process for the preparation of said slurry.